N parachute fabric

ABSTRACT

A parachute material utilizes a spunbonded web of continuous nylon filament autogenously bonded together at a substantial number of filament cross-over points, the web having an air permeability of from 300 to 550 ft3/min/ft2 and having a density of from 0.25 to about 0.46 g/cm3, to provide equivalent strengths at lower cost.

United States Patent 1191 1111 3,795,376

Stevenson et al. Mar. 5, 1974 [54] NON-WOVEN PARACHUTE FABRIC 3,252,676 5/1966 Fricder 244/145 3,531,067 9/1970 Mitchell... 244/145 [75] Inventors: 'K f 3,276,944 10/1966 Levy 161/150 Andrew M. Fallk, Rale1gh, both of N.C.

- Primary Examiner-George E. A. Halvosa M t C n St. L M [73] Asslgnee Oman 0 ompa y Oms 0 ASSlSlanl Examiner-Charles E. Frankfort [21] Appl. No.: 271,959

Related US. Application Data [62] Division of Ser. No 64,538, Aug. 17, 1970, [57] ABSTRACT abandoned.

A parachute material utilizes a spunbonded web of U.S. Cl. ontinuous nylon filament autogenously bonded to [51] Int. Cl. B64d 17/12, F42b 25/04 gether at a Substantial number f fu t 0530" [58] Field of Search 244/145, 152; points the web having an air permeability f f 30 102/35-356, 34.1, 37- to 550 ftWmin/ft and having a density of from 0.25 to about 046 g/cm", to provide equivalent strengths at [56] References Cited lower COSL UNITED STATES PATENTS 3,542,615 11/1970 'Dobo et a1. 156/181 4 Claims, 2 Drawing Figures 2.0 oz./ yd

AIR PERMEABILITY, cfm./f1. Gt O. 5in. H 0 0 1.0 OZ./yd.

0.6 OZ./yd.

0.7 oz./yd.

0.85 oz/yd.

FABRIC DENSITY, m./6m.

NON-WOVEN PARACHUTE FABRIC This is a division of application Ser. No. 64,538 filed Aug. 17, 1970 and now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention 'This invention relates to a parachute fabric and, more particularly, to a parachute fabric made from a spunbonded non-woven web of continuous nylon filaments being autogenously bonded together at a plurality of filament cross-over points, the nylon filaments and the unique bonding system providing the fabric with the high elastic recovery which is necessary if the fabric is to withstand the impact forces on deployment.

2. Description of the Prior Art Conventional parachutes made from light weight woven nylon cloth have beenknown in the art for several years; however, these chute materials suffer from the disadvantages of being costly due to the yarn spinning and weaving processes, difficult to fabricate into parachutes because of the raveling of the cut edges and the inability for the descent rate of the chute to be accurately controlled. For example, if the descent rate is too fast, the parachute must be deployed at an altitude which is too high for most efficient lighting in order that it will not arrive at the ground while still burning. For low descent rates, the particular parachute for delivering an equivalent weight of payload, must be very large.

The use of non-woven fabrics as a parachute material is unknown since the non-Wovens possessing adequate elastic recovery and shock resistance are too heavy, and therefore too bulky, to be inserted in the normal parachute canister. Furthermore, such non-woven fabrics would fail certain parachute performance tests for the reasons that the interfilament bonds do not approach the strength of the filaments themselves, the filaments do not possess a high elastic recovery during parachute deployment, and the degree of permeability can not be accurately controlled to provide a given descent rate. a

An example of a low descent rate, high intensity illuminating flare parachute is disclosed in U. S. Pat. No. 3,478,687 to Craig. In this patent, an attempt is made to transform a parachute into a hot air balloon using the heat of the flare to reduce the density of the air within the chute to lower the descent rate. Even though a lower descent rate may have been disclosed, once the parachute design is standardized, the descent rate cannot be altered.

SUMMARY OF THE INVENTION The present invention provides a unique fabric with a given air permeability which, for a given weight of fabric, is superior to any other parachute material now known in the art. The parachute material of this invention is a non-woven web which is comprised of continuous nylon filaments arranged within the plane of the fabric preferably without order. The filaments are autogenously bonded together at a substantial number of filament cross-over points such that the strength of the bond between the filaments approaches the strength of the filaments themselves. The web is made operable for parachutepurposes by being provided with an air permeability of from about 306 to 550 ft lminlft at 0.5

in. of water and by being provided with a web density of from about 0. 25 to O. 46 g/cm".

The nylon filaments comprising the parachute fabric are autogenously bonded together at a substantial number of filament cross-over points to provide multidirectional dimensional stability. The strength of the bond approaches that of the nylon fibers so that a force exerted on one portion of the fabric will be propagated throughout the fabric to a significant extent. Autogenously bonded means that the bonds between the filaments are formed in the absence of an external binder. For example, two filaments may be autogenously bonded together by the application of heat in that the fibers are fused at the cross-over points. Autogenous bonding also includes the use of solvents since upon the removal of the solvent from the filament, the polymers comprising the filaments are mixed at the filament cross-over points. However, the preferred method for autogenously bonding nylon filaments is set forth in U. S. Pat. No. 3,516,900. Thisbonding system employs a hydrogen halide gas and, more particularly, hydrogen chloride gas to effect bonding. The filaments absorb the hydrogen chloride gas along the surface areas which results in the breaking of the intermolecular hydrogen bond between adjacent amide groups. Upon desorbing the hydrogen chloride gas from the nylon filaments, the intermolecular hydrogen bond between amide groups of different fibers reforms resulting in bonding at interfilament cross-over points.

While the filaments comprising the fabrics may be completely undrawn, partially drawn, or completely drawn, it has been found that partially drawn nylon filaments are most effective for the reasons that the filament tensile strength is substantially greater than the tensile strength of the undrawn nylon and the elastic recovery properties of partially drawn nylon filaments is substantially greater than the elastic recovery properties of completely drawn nylon filaments since those filaments which are completely drawn have almost no elastic recovery properties. Thus, the use of partially drawn nylon filaments results in a suitable balance be tween filament tensile strength and filament elastic recovery properties.

The preferred rates of air permeability through the fabric will vary depending upon the type of fabric used, the conditions of deployment and the payload to be delivered. For the purposes of this invention, the air permeability of the spunbonded fabric must be between 300 and 550 ft /min/ft at O. 5 in. of water and must have a fabric density of from 0.25 to about 0.46 g/cm Density is a function of fabric weight and fabric thickness and it has been found that the weight of the fabric should be between 0.6 and 1.0 oz/yd and the fabric thickness should be between 1.7 and 5.3 mils. A density of less than 0.25 g/cm results in air permeability being greater than 550 ft/min/ft which is unsatisfactory since either the descent rate is too great or the fabric does not possess the strength, elastic recovery and toughness necessary to withstand the forces of deployment. At air permeabilities less than 300 ft /min/ft of fabric, either the weight or the thickness of the fabric becomes too great to be easily manageable in the packing of the canopy or the rate of parachute descent becomes too low especially when the payload is a flare which upon burning emits magnesium oxide. Mangesium oxide is the product of the combustion of the flare and becomes trapped between interstices of the filaments of the parachute to further reduce the descent rate to the degree that the blinded" parachute will actually rise due to the reduced air density within the chute which is caused by the heat produced upon flare combustion.

Therefore, an object of this invention is to provide a parachute material comprised of a spunbonded nonwoven nylon fabric.

Another object of this invention is to provide a spunbonded non-woven nylon parachute fabric with an air permeability of from 300 to 550 ft"/min/ft and with a fabric density of from 0.25 to about 0.46 g/cm.

Another object of this invention is to provide a spunbonded non-woven parachute material useful in the deployment of illuminating flares.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the relationship between the density and air permeability of the spunbonded non-woven parachute fabrics of this invention; and

FIG. 2 is a plan view of a cruciform canopy made from the spun-bonded non-woven parachute fabric of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Substantially all polyamide fibers may be used to form the spunbonded fabrics of this invention. For simplicity however, the nylon subsequently referred to is nylon 6, 6 which is prepared by condensing hexamethylene adipamide and adipic acid. Spunbonded nonwoven fabrics in the unbonded state may be made by many processes, one of which being set forth in U. S. Pat. No. 3,338,992. The melt extruder was used for spinning continuous nylon filaments. The formed filaments were then drawn downwardly away from the extruder by an aspirator which also deposited the filaments by means of moving air on a conveyor belt. The nylon filaments comprising the fabric were then bonded together to form the coherent fabric of this invention by being passed through a chamber containing a hydrogen chloride activating gas. The nylon filaments absorbed the hydrogen chloride which rendered them bondable upon the removal of the gas. Thus, the filaments were permanently bonded together at a substantial number of touching filament cross-over points by having the gas desorbed from the filaments either by heat or by water means. For the purposes of this invention, the fabric had a weight ranging between 0.6 and L oz/yd Within the given weight range, the fabric was provided with a thickness of from 1.7 to 5.3 mils by having passed the fabric between heated calender rolls which reduced the thickness from that in the uncalendered state to within the mentioned range. The combination of the fabric weight and the controlled degree of fabric thickness resulted in a fabric density ranging from 0.25 to about 0.46 g/cm.

Calendering to said thicknesses is done on a standard textile calender consisting ofa heated top steel roll and cotton filled bottom roll. Depending on the permeability desired, the temperature of the heated roll can range from 300 to 400F., at roll pressures from 1000 to 2000 pounds/lineal inch, and roll speeds of from 25 to 40 yards/min.

Density p is a function of weight, W, and thickness, T, and can be expressed by the formula p W/T. In reference to FIG. 1, the area within the block represents the fabric properties of this invention. For example, at an air permeability of 400 ft /min/ft fabric density can be increased or decreased by choosing different weight material. The particular weight. of course, would depend upon the ultimate end use of the fabric, for example. the design of the parachute, the weight of the payload and the like. Likewise, fabric density can remain constant and the air permeability increased or decreased by choosing different weight fabrics. By interpolation, the heaviest fabrics to be used for the parachute fabric of this invention, would be a little less than 2 oZ/yd whereas the lightest fabric would be approximately 0.4 oz/yd The density of the nylon spunbonded fabric of this invention prior to the calendering step is approximately 0.15 g/cm which remains constant regardless of the particular weight employed. Therefore, it can be seen that the spunbonded fabric without having been densified would not be operable for use as a parachute fabric.

In reference to FIG. 2, the nylon spunbonded fabric of this invention is constructed in the shape of a cruciform parachute canopy 10 which is comprised of a square-shaped center portion 15 and square-shaped flaps 11, 12, 13 and 14 which are co-extensive in size with center portion 15. Flaps ll, 12, 13 and 14, respectively, have edges l9, l6, l8 and l7joined to a selected edge of center portion 15 with the edges of the flaps being contiguous with the edges of the center portion. The specific construction of canopy 10 may vary; for example, flaps 11 and 13 and center portion 16 may be of one continuous strip with flaps 12 and 14 being joined thereto. Edges 21, 22, 23 and 24 which are opposed and parallel to edges 19, 16, 18 and 17, respectively, are provided with a plurality of grommets 25 to which shroud lines (not shown) are attached.

The parachute material of this invention, while not limited to, is ideally suited for the cruciform parachutes to which illuminating flares are attached as the payload. The curciform parachute descends with negligible oscillation of the payload which prevents the air trapped by the parachute from spilling out. The result is that the magnesium oxide which is the product of combustion of the flare is trapped by the filaments which results in the closing of the fabric interstices, i.e., small openings between filaments through which air normally passes. A round chute however, manifests an appreciable oscillation during descent resulting in the magnesium oxide vapors being spilled out before they ever reach the parachute fabric. The closing of the interstices results in reduced air flow through the fabric which coupled with the decreasing flare weight provides for a reduced descent rate. This results in a longer illumination time over the target area. Thus, it can be seen that where the density of the fabric is exceedingly high, (i.c., 0.46 g/cm) the magnesium oxide clogs the fabric interstices and actually causes a rising of the chute such that the smoke delivered upon combustion of the flare covers the flare and prevents proper illumination.

We claim:

1. A parachute canopy comprising a non-woven fabric, said fabric being comprised of continuous nylon filaments arranged in the plane of the web without a preferred order, said filaments being autogenously bonded together at a substantial number of touching filament cross-over points, said web having an air permeability of from 300 to 550 cubic feet per minute per square 5 6 foot at 0.5 in. H and having a web density of from 2. The parachute fabric of claim 1 wherein the weight 0.25 to about 0.46 grams per cubic centimeter, said of said web is from 0.6 to 1.0 ounce per square yard. canopy being connected to a flare to form a flare parachute, said flare upon burning emitting magnesium 3. The parachute fabric of claim 1 wherein the thickoxide which is trapped by said nylon filaments compris- 5 ness of said web is from 1.7 to 5.3 mils. ing the fabric to close a substantial number of inter- 4. The parachute fabric of claim 1 wherein the nylon stices within the fabric whereby. the descent rate of said filaments are partially drawn. flare parachute is reduced. 

2. The parachute fabric of claim 1 wherein the weight of said web is from 0.6 to 1.0 ounce per square yard.
 3. The parachute fabric of claim 1 wherein the thickness of said web is from 1.7 to 5.3 mils.
 4. The parachute fabric of claim 1 wherein the nylon filaments are partially drawn. 